This invention relates to a new gene, called don-1, related to growth factors such as the neuregulins, and methods of preparing and using alternate splice forms of this gene to express new Don-1 polypeptides. The invention also relates to the use of these new genes and corresponding polypeptides.
The growth, differentiation, and survival of many cell types depends on the binding of protein ligands to specific cell surface receptors. Misregulation of this interaction has been implicated in a wide variety of tumors and developmental irregularities. For example, the epidermal growth factor receptor (EGFR) family of receptor-type tyrosine kinases are frequently overexpressed, mutated, or deleted in carcinomas of the breast, lung, ovary, brain, and gastrointestinal tract (Prignent et al., Prog. Growth Factor Res., 4:1-24, 1992). This family of receptors, which includes receptors referred to as EGFR, erbB2 (also called "neu" or HER2, the human homolog of erbB2), erbB3 (HER3), and erbB4 (HER4), respectively, may play an important role in the modulation of tumor growth and progression. In particular, it has been shown in several studies that overexpression of erbB2 in a variety of human adenocarcinomas, e.g., in breast and ovarian cancer, correlates with a poor prognosis (see, e.g., Slamon et al., Science, 235:177-182, 1987).
One group of ligands that bind to this family of receptors is referred to as the neuregulin family of ligands, which all share a common structural domain known as an EGF motif that contains six cysteines. This motif not only allows these ligands to bind to the receptors, but to mediate biological effects as well (Barbacci et al, J. Biol. Chem., 270:9585-9589, 1995)). Although there appear to be multiple ligands capable of binding to and activating members of the EGFR family, the growth factors that bind to and activate the other members of this receptor family, erbB2, erbB3, and erbB4, are less well characterized.
Neuregulins are also referred to as neu differentiation factors (NDF), glial growth factors (GGF), heregulins, and acetylcholine-receptor-inducing activity (ARIA) ligands, all of which are expressed as variant splice forms of a single gene. These different names reflect the diverse biological activities of the neuregulins in vitro, as glial cell mitogens, receptor binding proteins, mammary differentiation factors, and muscle trophic factors.
Each of the neuregulin glycoproteins has been shown to activate one or more of the receptors erbB2, erbB3, and erbB4 (for a review, see Ben-Baruch et al., Proc. Soc. Exp. Biol. Med., 206:221-227, 1994). These factors were first purified on the basis of their ability to activate, i.e., cause phosphorylation of, the erbB2 receptor, although it has been shown subsequently that these factors do not bind erbB2 directly (Tzahar et al., J. Biol. Chem., 269:25226-25233, 1994). In addition, it has been shown that NDF causes the differentiation of human mammary tumor cells (Peles et al., Cell, 69:559-572, 1992).